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Home / Method Statements / Method Statement For Spool Fabrication Of Steel Piping

Method Statement For Spool Fabrication Of Steel Piping

The spool fabrication will be implemented with the sequence of marking, cutting, fit-up, welding, and painting.

Marking

All materials shall be marked for identification and traceability with respect to installation area, sheet number and spool number.

The cut pipe spools shall be marked with their respective spool numbers, in accordance with the marked up fabrication drawing.

The method used for marking shall not result in contamination of the Material, significant strain hardening, or sharp discontinuities.

Marking for cutting shall include all dimensions (diameter, Wall thickness, length) and the joint detail of drawings and be done exactly taking into consideration allowance for welding shrinkage and cutting loss.

In case the original identification markings are unavoidably cut out or The material is divided into two or more parts, the marking shall be Accurately transferred for each pieces prior to cutting to a location Where the marking will be visible on the completed spool.

Cutting and Edge preparation

Carbon steel shall be cut by method of flame cutters and stainless steel shall be cut by a plasma cutting machine If plasma arc cutting is done the following procedure is employed.

Large sized pipes (above 28″ NPS) and holes of branch connections shall be cut by a plasma cutting machine.

When cutting starts, if access permits, a receiving basket for spatters shall be inserted in the inner cutting area of the pipe to avoid adherence of spatters to internal wall of pipe.

If the cutting area is inaccessible, a spatter compound is applied to the inside cutting area by brush, roller or swab. The application of the compound is applied completely around circumference, a minimum of 200㎜ each side of the cutting area. After cut, the anti-spatter compound shall be removed by clothes or other methods.

All materials cut by a flame or arc shall have the edge ground back to clear the affected zone. The grinding wheel is marked by an impregnated red dye in the make-up of the disc which denotes chloride free material when used for stainless steel. Wire brushes with stainless steel bristles will be used, dedicated to stainless steel and high alloy materials. Files for use on stainless steels and non ferrous alloys shall be NEW and dedicated to a particular alloy only.

All edges shall be accurately maintained as per design requirement with a smooth even surface with all slag removed. Beveling will be performed with a grinder. Separate machines will be used for carbon steel and stainless steel. Preparation will be in accordance with the approved

The preparation of edge for welding shall be done by machining or grinding. Edge preparation shall be performed in accordance with the approved WPS. The surfaces of the edge shall be free from tears, grease, oil slag, scale or internal burrs. Stainless steel shall be beveled by grinding. Separate machines will be used for carbon steel and stainless steel.

Fit up Procedure

Alignment for the fit-up of the piping components shall be executed on a steel floor or steel jack stand for carbon steel spools. For stainless steel spool fabrication the floor will be covered with wooden planks or rubber. All stands will be insulated with clean rubber sheeting to prevent contamination of the spools. Under no circumstances shall stainless steel materials be allowed to come into contact with carbon steel.

Pipe shall be properly supported at least 150mm off the ground and aligned by jigs or clamps in order to eliminate strains prior to tack welding. Where jigs or clamps are used for stainless steel fabrication, these items will be lined with clean rubber or stainless steel material to eliminate the possibility of contamination with other project material.

The number of welds in a spool shall be kept to a minimum. Minimum spacing of circumferential welds between center lines shall not be less than four (4) times the pipe wall thickness, or at least 2 inches.

The bolt holes of flanges shall straddle the normal horizontal and vertical center line of pipe. Holes for attachment of weldolets and nippolets shall be performed using gas torch and all burrs shall be removed.

Adjacent sections of welded pipe that are joined by butt welding shall have the longitudinal weld seams positioned so that they are least 15 degrees apart.

Tack Welds

Prior to performing main welds, tack welds shall be done. Tack welds shall be made by qualified welders. The length and number of tack welds for the diameter of pipe being welded shall be specified as follows.

Permanent tacks of the desired penetration and workmanship, and conforming to need not be removed before welding unless handling may have caused the tacks to crack. Any crack tacks will be completely removed by grinding and grinding areas to be checked and approved.

Welding Procedure

All welds shall be performed in accordance with the approved WPS and Welding material control procedure which shall be displayed on a notice board close to the work.

Any cracks, blowholes, cold laps, unusual irregularities, slag, flux, or other impurities that appear on the surface of any welding bead shall be removed by grinding or chipping before depositing the next successive bead. In the case of submerged arc welding of carbon steel the removal method used may be air arc gouging, which shall be cleaned out by grinding to shiny metal.

The requirement of the finished weld reinforcement for all materials should comply with ASME B 31.3 specification for piping.

If arc strike occurs, this shall be removed by grinding with client’s prior approval. The ground area shall be inspected by MT (carbon steel) or PT (stainless steels).The remaining wall thickness shall not be less than the stipulated minimum, as stated in specification or ASME B 31.3 If pipe is ground severely to repair, the damaged part of the pipe shall be removed.

Internal purge of argon shall be used for the GTAW process root pass on stainless steels as specified by WPS. Purging will be carried out by using the best method for the particular application during welding. Each end of the pipe adjacent to the weld of tie in spools shall be dammed by using water soluble paper or sponges at a distance of 150㎜ from the weld.

purging of welding pipes

Branch connections and outlets

  • All welded branch connections shall be jointed to the header with full penetration welds.
  • Preparation for branch connections shall be jointed as per ANSI B 31.3, Fig. 328.5D and drawing.
  • Reinforcement pads or saddles required by specifications and drawings shall be of the same material as the main pipe (unless specified otherwise) and shall be formed and countered to provide a good fit to both main and branch pipe.
  • Branch reinforcement pads or each segment thereof shall be provided with a minimum 3.0 mm drilled and tapped whole prior to fitting to the pipe, so ensuring leak detection, venting and testing facilities. Whenever possible, pad should be made in one piece before fitting onto pipe.
    • In case of stainless steel marking shall be done with weather proof chalk (chloride free crayon), low chloride marking pen (less than 30 PPM) or engraving.
    • The method will be used for the permanent marking for welder identification, in lieu of marking the weld, appropriate records shall be filed as per approved inspection procedure.
    • After spool installation, testing and final reinstatement of stainless steels, all markings shall be removed using an appropriate solvent.
    • Welding material control. This shall be controlled by welding material control procedure

Qualification of welders and welding operators

  • Qualification of welders and welding operators shall be performed in accordance with qualification and control procedure of welders and welding operators. All welding procedures, welders & reference to be used shall be qualified in accordance with ASME B 31.3 paragraph 328.2
  • Performance qualifications will be carried out for all welders and welding operators in accordance with the requirement.
  • All welders should always keep their identification cards at all times with their name and number plus a photograph, signed by surveyor.
  • The qualification limits and ranges for WPS / PQR and welders will to be based on ASME B 31.3
  • The acceptability of the test weld shall be judged as follows. Visual inspection by inspector; Root bead and surface of weld. Burn thru during application of hot passes and subsequent passes, after visual acceptance, is cause for immediate disqualification Radiographic examination or bend test in accordance with ASME B 31.3.

Temporary Attachments

Piping fabrication shall be achieved by use of clamps, jigs, fixtures, without welding to the pipe or fitting. The use of cleats, bridge pieces, tacking strips or other attachments welded temporarily to pipe work to facilitate fabrication shall be of the same or equivalent material as the pipe work to which they are supposed to be attached. Initial fitting up can be achieved using temporary bridge tacks across the groove.

Threaded and Socket Welds

  • Threads shall be concentric with outside of pipe, per ANSI B 31.3, tapped and cleaned out.
  • All surfaces of threaded joints shall be checked before connection, and any dust, oxide and grease shall be removed.
  • When socket weld fittings are used, pipe shall be spaced approximately 1/16 inch (1.6 ㎜) away from the “bottom “of the socket. Minimum gap to be 3/64 inch (1.2 ㎜) and maximum to be 1/8 inch (3.2 ㎜)
  • A sealant for threaded piping can’t use Teflon tape except for hydraulics where fluid thread sealing material shall be utilized.
  • Screwed connections subject to seal welding shall be made without the use of sealing compound.
  • Seal welding of threaded connections shall be done by a qualified welder and seal welds shall cover all exposed thread.
  • The joint shall be cleaned of all cutting oil and other foreign material and made up dry to full thread engagement, before seal welding.
  • Thermo wells shall not be seal welded.
  • Seal welded and threaded piping shall not be substituted for socket weld piping connections without prior written approval by Company.
  • Unless otherwise stated on approved drawing or specifications, pipe Threads shall conform to ASME B 2.1

Material Segregation

  • Direct contact between carbon steel and stainless steels is not permitted.
  • Tools and wire ropes containing carbon steel, grinding wheels and discs contaminated with carbon steel shall not be used on stainless steel.
  • Tools to be used for fabrication of stainless steel and non-ferrous alloy piping and piping components shall be stored separately to avoid mixing with tools previously used on carbon steel fabrication work.

8.9 Tolerance

The dimensional tolerance shall be in accordance as follows.

Length       less than 12mm  12mm and longer
Distance of any two parallel or crossing centre lines ± 12mm ± 12mm
Centre to flange face
Flange face to flange face

Heat Treatment

Pipe Heat Treatment shall be performed in accordance with the approved Heat treatment control procedure Table 331.3.1 of ASME B 31.3 and approved WPS.

NDE and Repair of defects

  • Repair welding shall be performed in accordance with piping weld repair procedure and Inspection for welds shall be examined in accordance with ITP
  • All final examinations shall be performed after any required post weld heat treatment.
  • Root concavity is not permitted. (Too restrictive – follow ASME B 31.3 table 341.3.2, as applicable )
  • Undercut shall be limited the requirement of ASME B 31.3, Table 341.3.2 for industrial piping.welding fabrication of spool
  • The removal of defective areas shall be by machining, grinding, chipping or arc / air gouging followed by grinding at a depth of 2mm, and The resulting excavation shall be clean, free from scale and have a contour to permit ease in repair welding, and The repair groove shall be examined, using magnetic particle inspection to ensure that all defects are removed.
  • NDE and visual inspection for piping should be performed in accordance to ASME B 31.3 and NDE procedure.
  • All repairs and initial NDE will be completed prior to stress relieving of the pipe spools.
  • The surface of repair welding will be cleaned thoroughly before welding in accordance with applicable WPS.
  • Prior to repair welding, preheating around the repair area will be as per the approved WPS. Repair welding shall be performed in accordance with approved piping weld repair procedure and WPS

Protection and storage of pipe spools in pipe stock yard

  • Upon delivery of pipe, checks will be made to ensure that all end covers are in place to prevent ingress of dirt and moisture.
  • After final completion of carbon spool fabrication, carbon spools will be transferred to the painting area. Before transfer to painting area, spools should be blown thru or internally swabbed to remove contaminants.
  • After completion of painting, the spools shall be stored on wooden support. For preservation, all flanges and gasket surfaces shall be adequately protected e.g by plywood, plastic caps or equivalent methods before moving the pipe spools.
  • The Production Department will sort and select the spool as per the line system in order to install the spools on the module conveniently.
  • After completion of fabrication, stainless steel are transferred to the pipe stock yard directly and segregated from C.S spools.
  • Spools for installation; all pipe ends will be protected by plywood or equivalent methods attached to flanges.
  • All threaded nipples and bosses should be protected using waterproof tape or equivalent material to prevent damage to the threads.
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